A wide variety of elongated medical instruments that are adapted to be permanently or temporarily implanted in the mammalian body, usually the body of a human patient, or used to access a site in the body to facilitate introduction of a further medical device. Such elongated medical instruments have an instrument body extending between instrument body proximal and distal ends, and a distal segment of the instrument body is advanced to a remote site in the body by manipulation of a proximal segment of the instrument body or a handle or stylet or the like extending from the instrument body proximal end located outside the body.
Elongated medical instruments include implantable medical electrical leads, catheters, guidewires, stylets and the like. In the case of a medical electrical lead, the lead body proximal end is coupled to an implantable pulse generator (IPG) or monitor that is then implanted subcutaneously or to an external medical device located outside the body and electrical signals are conducted to or from the remote site in the body through one or more lead conductor. Catheters typically extend through the patient's skin and are coupled with external diagnostic or therapeutic equipment or are used to introduce other elongated medical instruments or fluids or the like, or to withdraw fluids or measure pressure, or the like, through a catheter lumen open at the accessed remote site. Certain catheters, e.g., electrophysiology ablation and mapping catheters, also deliver electrical energy or conduct electrical signals of the body. Other catheters include pulmonary artery catheters, central venous catheters, diagnostic coronary catheters, intra-aortic balloon pump catheters, balloon tipped (PTCA)/angioplasty catheters, and cardiac stent delivery catheters. The terms “catheter” and “lead” are often interchanged in these and other contexts.
Guidewires are small diameter wires that are directed through tortuous pathways to provide for advancement of open-ended medical leads or catheters having guidewire receiving lumens over-the-wire. Certain guidewires are also designed to function as a micro-catheter for infusion of fluids through a guidewire lumen. Other guidewires include insulated electrical conductors connected at the guidewire proximal end with an external medical device to deliver electrical energy for tissue stimulation or to conduct electrical signals of the body to the external medical device.
Stylets are small diameter wires that are inserted into lumens of closed end electrical medical leads to stiffen the assemble and provide directional control enabling the assembly to be advanced through pathways, e.g., transvenous pathways, in the body to lodge electrodes and/or sensors on the lead body at a desired site.
Hence, in the following discussion, the term elongated medical instrument relates to and embraces such electrical medical leads, catheters, stylets, and guidewires having directional control enabling deflection of a distal tip or inducement of a curve or bend in one or more distal portion of the instrument body from a proximal portion accessible outside the body.
In many cases, the introduction of such elongated medical instruments to a remote site in the body is effected through a skin incision accessing an incision into a blood vessel, whereby the instrument body is advanced through a vascular pathway until the distal segment or the instrument body distal end are located at the remote site. Such advancement is often through a tortuous pathway having twists and turns requiring the capability to impart a curve or deflect the instrument body distal end to facilitate advancement. Therefore, the introduction of such elongated medical instruments through vascular pathways or other tortuous pathways in the body is facilitated by a wide variety of techniques and mechanisms that have been developed to impart curves in the distal segment of the instrument body or to deflect the instrument body distal end.
Currently, during the implantation of a permanent cardiac pacemaker or an implantable cardioverter/defibrillator (ICD), endocardial cardiac leads, e.g., pacing leads and/or cardioversion/defibrillation leads, are introduced into a vein either via a cut down or percutaneous sheath introduction. The cardiac leads are advanced under fluoroscopy into either the right atrium, right ventricle (or both in the case of a dual chamber pacemaker or ICD implantation) or into a cardiac vessel, e.g., the coronary sinus and great vein. Generally speaking, it is highly desirable that such cardiac leads be so flexible through their length that they are capable of flexing with the movement of the heart and other muscular movement so as to void the fracture of the lead body due to its cumulative stressing. Such cardiac lead bodies are generally too limp to be advanced axially on their own through the vascular pathway to the desired site in a heart chamber or vessel. It has been commonplace for many years to employ thin wire stiffening stylets extended down a lumen of the lead body to stiffen the entire assembly so that it can be pushed axially through the venous pathway: Then, the distal pace/sense electrodes or cardioversion/defibrillation electrodes (herein “cardiac electrodes”) must be fixed at the preferred site in the heart chamber or vessel to operate most efficaciously and to prevent dislodgement. The introduction and fixation of these cardiac leads is the most time consuming and difficult aspect of the implantation.
At the outset, a straight or slightly curved stiffening stylet is first extended into the lead body lumen within the cardiac lead in order to give the cardiac lead sufficient column strength and rigidity to be pushed through the tributary veins and typically into the subclavian vein. The stylet may be left straight or provided with a certain degree of curvature to facilitate the introduction through these veins and through the initial curvatures thereof. Thereafter, and from time to time, as the physician directs the distal tip of the cardiac lead in a tortuous path leading to the right heart through the superior vena cava (SVC), it may be necessary to withdraw the stylet and either substitute a new stylet or impart a different curvature to the distal segment of the stylet, reinsert the stylet, and advance the distal segment of the lead a bit further until another obstacle to advancement is encountered.
When the distal cardiac electrodes are to be placed in the right ventricle, the physician manually fashions a curve at the tip of another stylet that is inserted into the lead body lumen to advance the assembly through the tricuspid valve into the right ventricle. Most physicians continue advancing the lead with the curved tip stylet in place into the pulmonary artery outflow track to confirm right ventricle access and to rule out the possibility of entrance into the coronary sinus or coronary vein, which can mimic the appearance of a right ventricle placement under fluoroscopy. The conventional practice requires the physician to then remove the curved stylet and partially re-advance the original or another straight stylet into the lead body lumen, once the physician has confirmed that the lead is in fact in the pulmonary outflow track. The cardiac lead is then carefully pulled back under direct fluoroscopic observation until the lead body distal segment drops from the proximal portion of the pulmonary artery to the floor of the right ventricle. The physician then advances the stylet to its fully advanced position within the lead body lumen and advances the lead distal end into the right ventricular apex. Passive or active fixation mechanisms at the lead body distal end then effect fixation with the trabeculae or the myocardium to acutely maintain the cardiac electrode(s) at the operative site.
In the case of atrial lead placement, the lead body distal end is typically lodged or affixed in the right atrial appendage which results in the lead body extending into the right atrium via the SVC and then bent through about a 180° or greater bend.
Over the years, many atrial cardiac lead designs and atrial cardiac lead introduction tools and techniques have been proposed or clinically used to both achieve this orientation and to fix the cardiac lead body distal end within the atrial appendage and avoid dislodgement. Initially, such atrial cardiac leads were formed with a permanent “J”-shaped bend to facilitate both the positioning and the retention of the atrial electrode in the patient's atrial appendage as taught, for example, in U.S. Pat. No. 4,136,703. Insertion of these “J”-shaped leads is greatly facilitated through the use of a straight solid inner stylet which, in this case, straightens the bend normally fixed within the distal end of the lead itself to the extent that the stylet is advanced into or retracted from the lead body lumen.
Moreover, it has been proposed to combine atrial and ventricular leads together or in a cooperative relation to provide a “single pass” implantation of both leads as set forth in U.S. Pat. Nos. 4,458,677 and 4,479,500 and patents referenced therein. Such proposed single pass AV leads have not gained acceptance due to their complicated construction, use and size.
J-shaped atrial leads have largely been abandoned in favor of reduced diameter lead bodies that cannot accommodate shape-forming structures and the use of the straightening stylet as described above. Today, the small diameter cardiac lead body is normally straight, and the lead body distal end is typically aimed into the atrial appendage employing multiple insertions of relatively straight and curved stylets. The electrode bearing lead body distal end is fixed in the atrial appendage by means of an active fixation screw or passive fixation tines. However, dislodgements can occur before the fixation is effected when a stylet is withdrawn proximally as the stylet may bind against the lead body lumen in the region of the bend.
Thus, there are multiple exchanges of straight stylets and curved stylets, which have been bent according to the physician's choice in a typical cardiac lead implantation in the right atrium and ventricle. Similar techniques and multiple stylets are avoided to advance a cardiac lead distal segment into the coronary sinus and great vein. Stylets are typically formed of solid wire, typically about 0.014-0.018 inches in diameter. During handing, such stylets can easily become bent or kinked, and thereafter cause great difficulty when an attempt is made to reinsert them through the narrow inner diameter of the lead body lumen, which may only be 0.019 inch in the case of a stylet of 0.018 inch diameter, thereby providing no more than 0.0005 inch clearance around the circumference. The continual withdrawal and reintroduction of stylets is time consuming and offers the potential of damaging the lead in the process.
Moreover, it is undesirable to contaminate the lead body lumen with blood during this process because drying blood can form a strong adhesive bond between the stylet and the lumen wall, making stylet removal impossible and rendering the lead unusable. Because the surgeon is working through an open wound, even the most fastidious surgeon will have blood on his gloves that can be transferred to the stylet. The blood congeals, and because of the small clearance, even a few drops of blood are sufficient to causing jamming of the stylet inside the lead body lumen. When the stylet jams in the lead body lumen, kinking of the stylet within the lead can occur, which kinks, in turn, will create new jams or problems with the insertion and retraction of the stylet from the lead body lumen. In some cases, the jamming is so severe that the cardiac lead must be removed from the heart for fear of insulation puncture, discarded, and a new lead implanted, thereby at least doubling the lead cost used in the procedure as well as operative time. The overall result of such difficulties is that operative time is greatly increased which results in increased time delay, associated cost, and prolonged X-ray exposure to the patient under continuous fluoroscopy as well as prolonged scattered X-ray exposure to the operating room staff due to procedural time delays. These problems with the use of multiple stiffening stylets have been recognized in the art as set forth in U.S. Pat. Nos. 4,136,703, 4,381,013, 4,677,990, 5,662,169, 5,824,031, and 6,059,739, for example.
Many proposals have been advanced to reduce the number of stylets and the consequent number of times that stylet removal and re-insertion that are needed in the procedure. One approach has been to employ deflectable stylets wherein the stylet distal segment can be deflected or curved while within the lead body lumen from the proximal end thereof. Two-piece stylets that comprise a straight, tubular outer member and a curved inner member received within the outer member lumen enabling relative movement of the inner and outer members are disclosed in the above-referenced '703 and '013 patents for straightening a J-shaped bend and in U.S. Pat. Nos. 5,722,425 and 5,728,148. The outer tubular member of the '013 patent enables the transmission of torque applied by the implanting physician at the proximal end to be transmitted to a fixation helix located at the lead body distal end lead to screwed the helix into endocardial tissue. Alternatively, two-piece stylets comprising a curved outer member and a relatively straight inner member are also known to the art, as disclosed in U.S. Pat. Nos. 4,676,249 and 5,040,543. In such composite stylets, the relative position of the inner member with respect to the outer member determines the degree to which the curved member (inner or outer) is allowed to display its preset curvature.
A commonly employed approach to providing controllable deflection of the distal end segments of catheters and guidewires employs a generally straight outer sheath and a pull or push or push-pull wire extending through a lumen of the outer sheath to an attachment point at the sheath distal end. The wire is pushed or pulled on at its proximal end typically through a handle that is permanently or removably attached to the catheter or guidewire proximal end. The proximal retraction or distal advancement of the pull or push wire, respectively, causes at least a distal segment of the outer sheath to bend or deflect. Examples of such deflection mechanisms in catheters can be found in U.S. Pat. Nos. 3,547,103, 3,521,620, 4,815,478,4,898,577, 4,940,062, 5,125,395, and 5,545,200. U.S. Pat. Nos. 4,815,478 and 4,940,062 disclose the use of push-pull wires extending through guidewire lumens for deflecting the guidewire distal end by manipulating a handle at the guidewire proximal end. Deflectable stylets intended to be inserted into cardiac lead body lumens employing this type of deflection mechanism are disclosed in U.S. Pat. Nos. 5,662,119, 5,170,787, and 5,327,906, 5,396,902, 5,439,006, 6,059,739, and 6,146,138.
Spring wire guidewires and/or stylets are disclosed in the above-referenced '395, '620, and '338 patents that have pull wires extending from a proximal handle at the proximal end of the stylet or guidewire shaft through the lumen of the coiled wire body or shaft and to an attachment at the distal end of the coiled wire shaft. It is desirable to be able to control the direction of deflection of the distal segment so that it always bends in a known direction when the pull wire or push-pull wire is retracted or extended from the proximal handle. Linear attachment mechanisms are also provided in the distal segments of the coiled wire shaft that attach the adjacent coils together in a line parallel to the segment of the pull wire extending through the lumen so that the coil turns cannot be stretched apart or compressed together along that side of the segment. In the '620 patent, a short wire is disposed in and partially obstructs the lumen, and the coiled wire turns are welded to it. Several linear attachment mechanisms, characterized as “backbone” members, are disclosed in the '338 patent that are shaped to extend between the coil turns and to minimize the obstruction of the lumen. In the '395 patent, the coil turns are soldered together in the line. A further U.S. Pat. No. 5,931,830 discloses spot welding adjacent coils together to increase torqueability of a coiled wire guidewire rather than to control its direction of bending.
In a further variation, U.S. Pat. No. 5,477,856 discloses several embodiments of torqueable tubular members that are formed of a tube having one or more pull wire extending through the tube lumen to one or more distal attachment point. Segments are cut away from the stainless steel or shape memory alloy tube leaving a backbone bridging the cut away segment that is bendable upon retraction of the pull wire(s). In at least one embodiment, a plurality of adjoining cutaway tube segments are formed that are radially displaced by 30°-120°, for example, from one another to form a flex segment. A further plurality of flex segments, having the same number or differing numbers of cutaway tube segments are formed along sections of the tube. The cutaway tube segments can have the same or differing widths and separations apart from one another.
While all of the mechanisms disclosed in the above cited prior art patents are at least to some degree workable, there is still a perceived need for a mechanism that is simple, inexpensive to manufacture, does not excessively increase the elongated medical instrument body diameter, and can be manipulated using one hand to control the deflection and imparted curvature of the instrument body distal segment
More significantly, there is a need for a such a mechanism that eliminates the need for separate curved stylets used to deflect and impart curves in the medical instrument distal segment and which provides a wide degree of dynamic curvature to the elongated medical instrument being advanced by the physician.